Reflex Repeat HER2 Testing of Grade 3 Breast Carcinoma at Excision Using Immunohistochemistry and In Situ Analysis

Abstract

Our series demonstrated a high concordance rate (97%) for HER2 at excision in grade 3 breast tumors with a negative core biopsy result. These findings suggest that reflex repeat HER2 testing of all these cases, which has significant cost and workload implications, may not be justified. Features that may indicate HER2 heterogeneity, such as equivocal IHC on CNB specimens or tumor upgrade at excision, may help refine selection of cases for repeat testing.